Dimorphic Modification of the Trinuclear Nickel(II) Complex [Ni3(NCS)6(pdz)6]: Synthesis,Crystal Structure,Thermal, Magnetic and Spectroscopic Properties

Reaction of nickel(II) thiocyanate and pyridazine (pdz) as organic spacer ligand leads to the formation of the ligand‐rich 1:2 (1:2 = metal to ligand ratio) trinuclear nickel(II) complex of composition [Ni₃(NCS)₆(pdz)₆]. Depending on the reaction solvent, different polymorphic modifications are obtained: Reaction in acetonitrile leads to the formation of the new modification 1I and reaction in ethanol leads to the formation of modification 1II reported recently. In their crystal structures discrete [Ni₃(NCS)₆(pdz)₆] units are found, in which each of the Ni²⁺ cations exhibits a NiN₆ distorted octahedral arrangement. The central Ni²⁺ cation is coordinated by four bridging pdz ligands and two thiocyanato anions in trans positions. Both thiocyanato anions exhibit the end‐on bridging mode. The peripheral Ni²⁺ cations are bridged by one thiocyanato anion and by two pdz ligands with the central Ni²⁺ cation. Further they are coordinated by two terminal N‐bonded thiocyanato anions and one terminal N‐bonded pdz ligand. The structure of 1I was determined by X‐ray single crystal structure investigation and emphasized by infrared spectroscopy. Magnetic measurements revealed a quasi Curie behavior with net ferromagnetic interactions for 1I and net antiferromagnetic interactions for 1II . Solvent‐mediated conversion experiments clearly show that modification 1I represents the thermodynamic most stable form at room temperature and that modification 1II is metastable. On thermal decomposition, both modification transform quantitatively in a new ligand‐deficient intermediate. Elemental analysis revealed a 3:4 compound of composition [Ni₃(NCS)₆(pdz)₄]. A structure model supported by IR spectroscopic investigations was assumed, in which three coordination modes of the thiocyanato anion exist, resulting in a 2D polymeric network.     

Die Kristallstrukturen der Cyanidofluoridoborate K[BFx(CN)4–x], x = 0–4

The crystal structure of K[BF₃(CN)] (Pbcn (Nr. 60) with a = 13.3486(15) b = 6.5239(7) c = 10.0085(11) Å, and eight formula units per unit cell) has been determined and the one of K[BF₂(CN)₂] was confirmed and improved. The different networks in the complete series of borates K[BF_x(CN)_4–x], x = 0–4 are compared and discussed.     

On the electron affinities of ethylene and 1,3-butadiene

Temporary negative ion formation in ethylene and 1,3-butadiene has been studied using high resolution, low energy electron scattering. Sharp structure in the total electron scattering cross section allows the adiabatic electron affinity of each molecule to be determined leading to values of ?1.55 ± 0.1 eV for ethylene and ?0.62 ± 0.05 eV for 1,3-butadiene.     

Identification of 1,3-dialkylimidazolium salt supramolecular aggregates in solution

The nature of the interactions between 1,3-dialkylimidazolium cations and noncoordinating anions such as tetrafluoroborate, hexafluorophosphate, and tetraphenylborate has been studied in the solid state by X-ray diffraction analysis and in solution by (1)H NMR spectroscopy, conductivity, and microcalorimetry. In the solid state, these compounds show an extended network of hydrogen-bonded cations and anions in which one cation is surrounded by at least three anions and one anion is surrounded by at least three imidazolium cations. In the pure form, imidazolium salts are better described as polymeric supramolecules of the type {[(DAI)(3)(X)](2+)[(DAI)(X)(3)](2-)}(n) (where DAI is the dialkylimidazolium cation and X is the anion) formed through hydrogen bonds of the imidazolium cation with the anion. In solution, this supramolecular structural organization is maintained to a great extent, at least in solvents of low dielectric constant, indicating that mixtures of imidazolium ionic liquids with other molecules can be considered as nanostructured materials. This model is very useful for the rationalization of the majority of the unusual behavior of the ionic liquids.     

Preparation, crystal structure, absolute configuration, and conformational analysis of (−)436-(S)-(−)-diphenyl-1-phenylethylaminophosphine(η-pentamethylcyclopentadienyl)-dimethylphosphonato)cobalt(III)

Reaction of CpCoI₂(P(OMe)₃) 8 with the chiral aminophosphine (S)-(−)-diphenyl-phenylethylaminophosphine affords the diastereomeric phosphonate complexes (R,S)_Co,S_C-CpCoI(P(0)(OMe)₂)(PPh₂NHCH(Me)Ph) (10a,10b) via Arbuzov dealkylation. 10a,10b are separable and configurationally stable in solution for extended periods. The structure and absolute configuration of the lower R_f diastereomer (−)-₄₃₆-10b were determined via single-crystal X-ray diffraction. It crystallizes as a toluene solvate in space group P2₁ with a 13.194(6), b 9.062(4), c 17.023(5) Å, β 108.78(3)°, Z = 2, and was refined to R = 0.067 for 6318 reflections. Spectroscopic and structural evidence demonstrate a strong 1,6 intramolecular NH O=P hydrogen bond between the aminophosphine NH and the basic phosphoryl oxygen, which establishes a quasi-boat conformation. Proton nuclear Overhauser difference spectra show that the conformation in solution is the same as that observed in the solid state.     

6‐Acetonyldi­hydro­avicine

The title compound, 1‐(5‐methyl‐5,6‐di­hydro­[1,3]­dioxolo­[4′,5′:4,5]­benzo­[c][1,5]­dioxolo­[4,5‐j]­phenanthridin‐6‐yl)­acetone, C₂₃H₁₉NO₅, isolated from the stem bark of Zanthoxy­lum rhoifolium, crystallizes as a racemate in space group P. The structure shows two aromatic ring systems, each terminated by a five‐membered dioxole ring, coupled by an N‐containing ring. The core of the mol­ecule is almost planar; the planes of the two ring systems form an angle of 18.42 (6)°. The packing shows the mol­ecules parallel to each other and about 3.5 Å apart with graphite‐type interactions. The N‐methyl and acetone groups, which are anti with respect to one another, lie out of the plane and pack in spaces between neighbouring mol­ecules.     

Tellurium‐Halogen Secondary Bonding in the Crystal Structures of [Q]+[PhTeCl4]— (Q = C5NH6, 2‐Br‐C5NH5, {2‐Br‐C5NH5}{Co(NH3)4Cl2})

The reaction of diphenylditelluride with pyridine, 2‐bromopyridine or 2‐bromopyridine/tetraamminedichlorocobalt(III) chloride in 12 M hydrochloric acid afforded the tetrachlorophenyltellurate(IV) compounds [C₅NH₆][PhTeCl₄] ( 1 ), [2‐Br‐C₅NH₅] [PhTeCl₄] ( 2 ), and [{2‐Br‐C₅NH₅}{Co(NH₃)₄Cl₂}] [PhTeCl₄]₂ ( 3 ). They were all characterized structurally by single crystal X‐ray diffraction. In all structures, the arrangement about the tellurium atoms is square pyramidal. The [PhTeCl₄]^— anions in 1 and 2 form trimeric and dimeric units, respectively, through Te···Cl secondary bonding. Compound 3 shows an unusual face‐to‐face packing of the [PhTeCl₄]^—anions with hydrogen bonding to the bromopyridium cation.     

C-H-pi interactions in 1-n-butyl-3-methylimidazolium tetraphenylborate molten salt: solid and solution structures

The crystal structure of 1-n-butyl-3-methylimidazolium tetraphenylborate molten salt (1) shows C-H-pi interactions between the hydrogens of the imidazolium cation and the phenyl rings of the tetraphenylborate anion. The imidazolium ring is surrounded by three tetraphenylborate anions that are connected with the same cation by C-H-pi (phenyl rings) interactions. The nearest inter-ion interaction is found between the N-CH-N proton of the cation and the B-phenyl centroid (2.349 A) with a nearly T-shaped geometry. The inter-ionic solution structure of 1 has been investigated by the detection of inter-ionic contacts in 1H NOESY NMR spectra between the protons of the cation and the anion. The 1H-NMR spectra of molten salt 1 is almost independent of its concentration in [D6]DMSO solution, the imidazolium proton chemical shifts are in the expected region and there are no observable NOE effects between the protons of the cation with those of the anion, indicating that 1 behaves in [D6]DMSO as a solvent-separated ion pair. In CDCl3 the 1H-NMR spectra of 1 are concentration dependent and all the imidazolium protons are shielded as compared with those observed in [D6]DMSO. Moreover, the 1H NOESY NMR spectra show all the peaks affected by the interaction between the protons of the imidazolium cation and those of the anion, indicating that in CDCl3 1 possesses a contact ion pair structure. The NCHN proton of the cation exhibits the greatest shielding (up to -4.5 ppm). an indication of the existence of C-H-pi interactions, even in solution. The calculated distance of this proton to the phenyl centroid is 2.3 A for a C-H -pi angle of 180 degrees. The apparent volumes for the cation and anion, calculated from the measured 13C-NMR relaxation times, increase from 38 and 140 A3 in [D6]DMSO to 360 and 600 A3 in CDCl3, respectively; this indicates the formation of floating aggregates of the type (1)(n) in CDCl3 via weak hydrogen bonds, with increasing concentration.     

Are there pi* shape resonances in electron scattering from phosphate groups?

The temporary anion states of trimethyl phosphate and several compounds bearing the P=O group were explored using electron transmission spectroscopy and ab initio calculations to determine if these states have the characteristics of the pi* resonances usually associated with multiple bonds. No evidence was found for this in (CH3O)3PO and, by extension, we do not expect them to appear in the phosphate group of DNA. Cl3PO, however, does display such characteristics to some extent, and we show that they arise from the spatial properties of the sigma* (P-Cl) orbitals rather than from multiple PO bonding. A novel computational means to explore effects due to the relative size of a molecular orbital and that of the angular momentum barrier responsible for confining the additional electron is presented.